Study by infrared spectroscopy of the interaction of bovine myelin basic protein with phosphatidic acid.

Abstract

The effect of bovine myelin basic protein (MBP) on dimyristoylphosphatidic acid (DMPA) and phosphatidic acid prepared from egg yolk phosphatidylcholine (EPA) has been investigated by transmission and attenuated total reflectance (ATR) Fourier transform infrared spectroscopy. Interaction of MBP with DMPA and EPA dispersions decreases the lipid acyl chain conformational disorder as a consequence of hydrophobic interactions of the protein with the lipids. Since these effects are more important for EPA dispersions than for DMPA, MBP is believed to penetrate more into EPA bilayers. This could be due to the fact that the hydrogen bond network formed by the charged polar headgroups of EPA is weaker than that of DMPA. This is supported by the spectra of the phosphate region showing that the phosphate groups of EPA are less hydrogen bonded than DMPA. In the presence of MBP, the hydrogen bond network is replaced by electrostatic interactions of the protein with the polar headgroups of the lipid. Infrared spectra of the polar headgroup region also show evidence that MBP enhanced the second ionization state of the phosphate group at neutral pH, this effect being more important for EPA than for DMPA bilayers. Also, infrared spectra of the lipid carbonyl stretching region show evidence that MBP limits the accessibility of water molecules to the interfacial part of the lipid bilayer. Finally, ATR measurements on oriented films of lipid/protein complexes indicate that the penetration of the protein into the lipid bilayer is followed by a reorientation of the lipid acyl chains toward the normal to the bilayer in the case of EPA.(ABSTRACT TRUNCATED AT 250 WORDS)